Japanese Patent First Publication No. 2010-287455 discloses a solenoid device made up of magnetic coils which are energized to produce a magnetic flux, a plurality of plungers, stationary cores made from soft magnetic material.
The above solenoid device is designed to energize magnetic coils to generate a magnetic force and attract the plungers to the stationary cores. Springs are disposed between the plungers and the stationary cores. When the magnetic coils are deenergized, so that the magnetic force is lowered, the elastic force of the springs move the plungers away from the stationary cores. In this way, the plungers are moved forward or backward. The solenoid device is used in opening or closing, for example, a switch or a valve with the forward or backward movement of the plungers.
There are solenoid devices which have two modes: an individual attraction mode in which a plurality of plungers are individually attracted to a stationary core in a predetermined sequence and a simultaneous attraction mode in which the plungers are attracted to the stationary core simultaneously. The individual mode is used, for example, in turning on respective switches in sequence to check whether electric current will flow through a circuit or not, thereby inspecting whether the turned off switches are stuck or not. The simultaneous attraction mode is used in turning on a plurality of switches simultaneously to supply electric power to electric devices.
In order to perform the above two operation modes, the solenoid device is equipped with a plurality of magnetic coils. Each of the magnetic coils has a single plunger disposed in the center thereof. In the individual attraction mode, the magnetic coils are individually energized in a given sequence to attract the plungers, respectively. In the simultaneous attraction mode, the magnetic coils are energized simultaneously to attract all the plungers at the same time.
However, the above solenoid devices face a big problem in that in the simultaneous attraction mode, the magnetic coils are energized simultaneously, thus resulting in an increase in power consumed by the magnetic coils.